JP2953350B2 - Method for manufacturing molten carbonate fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell using an electrolyte, and more particularly to a molten carbonate composed of a molten carbonate such as lithium carbonate as an electrolyte and a lithium aluminate as an electrolyte holding material. Fuel cell.

[0002]

2. Description of the Related Art A conventional molten carbonate fuel cell is disclosed in, for example, JP-A-59-217956 and JP-A-61-1933.
No. 47 discloses a method in which a mixed slurry of lithium aluminate, ethanol and polyvinyl butyral is formed into a sheet, and is disclosed in JP-A-60-72172 and JP-A-60-817.
No. 72, JP-A-1-206568 and the like disclose a molding method by an aqueous papermaking method. On the other hand, JP
JP-A-1-147459 and JP-A-62-51166 disclose a method of forming an electrode catalyst layer from a fluororesin and hydrophobic carbon.

[0003]

However, the above-mentioned prior art does not disclose measures against moisture absorption of carbonates and deformation due to the influence thereof, and does not particularly consider handling of raw materials and electrolyte layers. Things. That is, the carbonate as the electrolyte and the lithium aluminate as the electrolyte holding material have extremely strong hygroscopicity. Therefore, the handling of not only moisture absorption during storage of carbonates and lithium aluminates as raw materials, but also absorption of moisture during the manufacturing process and storage of the electrolyte layer as a semi-finished product manufactured from these raw materials, We need to keep this in mind.

[0004] When the carbonate absorbs moisture, the lithium aluminate is affected by the moisture, and the electrolyte layer is deformed by warping, undulation, or unevenness due to a hydration reaction or the like.
In addition, the crystal phase of lithium aluminate is altered and cracks are generated in the electrolyte layer. Therefore, it is difficult to manufacture a high quality electrolyte layer. Furthermore, cross-leakage of the reaction gas and outflow of the electrolyte from the battery during operation, or an increase in the internal resistance of the battery occur, causing variations in performance, a decrease in the performance, and a decrease in the service life. Further, once the electrolyte layer absorbs moisture, it takes a long time to dry the electrolyte layer, which causes a rise in manufacturing cost.

Accordingly, it is an object of the present invention to suppress the moisture absorption of carbonate, prevent the deterioration of lithium aluminate, and easily and inexpensively produce a high quality electrolyte layer. That is, to facilitate the quality control of the carbonate and lithium aluminate or the electrolyte layer, economically produce a highly reliable electrolyte layer, and provide a molten carbonate fuel cell having stable performance and life. is there.

[0006]

The object of the present invention is to provide a method of manufacturing a molten carbonate fuel cell containing a carbonate as an electrolyte and a lithium aluminate as an electrolyte holding material.
This is achieved by rendering the carbonate and lithium aluminate hydrophobic with a hydrophobizing material.

[0007] Specifically, <br/> Oite method of manufacturing a molten carbonate fuel cell comprising an electrolyte layer composed of a carbonate as an electrolyte lithium aluminate as an electrolyte holding material, the electrolyte layer, a hydrophobic carbonate previously hydrophobized by the carbonate hydrophobizing material, the lithium aluminate is molded preliminarily hydrophobized hydrophobic lithium aluminate in each sheet by hydrophobing material hand
The molten carbonate fuel cell characterized by being superposed
This is achieved by a manufacturing method .

[0008]

By making the carbonate and lithium aluminate hydrophobic, the raw materials of carbonate and lithium aluminate and the moisture absorption of the electrolyte layer made therefrom are suppressed, so that the deterioration of the electrolyte layer and Deformation is prevented, the quality of the electrolyte layer is improved, and battery performance is stabilized and battery life is improved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various descriptions have been made on electrolyte layers for molten carbonate fuel cells made from carbonate and lithium aluminate. Conventionally, the effect of moisture absorption of carbonate on changes in the physical properties of the electrolyte layer has been described. The problem was not considered at all. Therefore, the present inventors have conducted various studies to solve the problem. For example, a sheet of 0.5 mm was prepared by a doctor blade method using lithium aluminate as a raw material, using tetrachloroethylene and trichloroethylene as a solvent, and adding polyvinyl butyral as a binder. To this sheet, a carbonate in which lithium carbonate and potassium carbonate (62:38 mol% ratio) were mixed was applied in the form of a paste with polyethylene glycol to form an electrolyte layer. Then, the performance of the battery comprising the electrolyte layer was evaluated.

However, it has been found that there is a large difference in battery performance due to a difference in the raw material lot of the electrolyte layer, a difference in the production date, or a difference in the number of storage days. As a result of examining the cause, it was found that the amount of water contained in the electrolyte layer had a large effect. Therefore, the electrolyte layer was manufactured in a constant temperature and constant humidity, but the product variation was reduced but not sufficient. It has been found that the cause is that there is a limit to the humidity control at the electrolyte layer manufacturing site and that the battery assembly takes a long time to gradually absorb moisture and adversely affect the electrolyte layer.

[0011] When the electrolyte layer absorbs moisture, a hydration reaction or a hydrolysis reaction occurs in the lithium aluminate, causing "slipping" or "undulation" in the electrolyte layer, which causes cracking.
It has also been found that the electrolyte layer becomes coarse and pores, and cross-leak of the reaction gas occurs inside the battery, and the internal resistance increases, which causes a reduction in performance and life. Eventually,
In order to produce a highly reliable electrolyte layer, it is necessary to mold the electrolyte layer so as not to absorb moisture. For example, carbonate and lithium aluminum which are raw materials of the electrolyte layer are used.
It has been found that hydrophobizing the gel is most effective. Then, it was confirmed that a high quality electrolyte layer can be produced by preventing the carbonate and lithium aluminate from absorbing and deforming during the manufacturing and storage of the electrolyte layer or during the battery assembly process.

Next, an embodiment according to the present invention and an experiment for confirming the embodiment will be shown and described in further detail. Embodiment 1 FIG. FIG. 1 is a sectional view showing a molten carbonate fuel cell according to one embodiment of the present invention. Embodiment 1 FIG. Is the configuration shown in FIG. Example 2. And 3. Is also the same as the configuration shown in FIG.

Lithium carbonate / potassium carbonate (62:38)
Molar% ratio) To 42 g of the mixed powder and 58 g of γ-lithium aluminate powder (specific surface area: 23 m ² / g), 5.3 g of polytetrafluoroethylene powder of a fluororesin was added, and mixed for 3 hours with a vibration mill to obtain hydrophobicity. It has become. That is, a material capable of forming a hydrophobic electrolyte layer was prepared. Then at 350 ° C 5
Time Heated and dried quickly. To this, 30 g of polyvinyl butyral, 94 ml of methanol, 142 ml of n-butanol and 10 ml of butyl butylphenol glycolate were added.
The resulting mixture was kneaded with a ball mill for 15 hours at room temperature to prepare a slurry having a viscosity of about 120 poise.

The slurry was degassed under reduced pressure by a vacuum pump, and then was 0.4 mm thick and 200 mm wide by a doctor blade method.
To form a sheet-like electrolyte layer 3 as a hydrophobic electrolyte layer. In addition, it is not restricted to the shape of a sheet. Then, the electrolyte layer 3 was sandwiched between the anode electrode 2 and the cathode electrode 4 and further laminated by the separators 1 and 5 to complete a molten carbonate fuel cell.

Embodiment 2 FIG. 42 g of lithium carbonate / potassium carbonate (62:38 mol% ratio) mixed powder and 58 g of γ-lithium aluminate powder (specific surface area: 23 m ² / g)
Then, 5.3 g of stearic acid as oils and fats was added thereto, and the mixture was mixed with a vibration mill for 3 hours to make it hydrophobic. Then 80 ° C
For 5 hours. To this, 30 g of polyvinyl butyral, 94 ml of methanol, 14 n-butanol
2ml and butyl phenol glycolate 10ml
Was added and kneaded with a ball mill for 15 hours at room temperature to prepare a slurry having a viscosity of about 120 poise.

The slurry is degassed under reduced pressure by a vacuum pump and then 0.4 mm thick and 200 mm wide by a doctor blade method.
To form an electrolyte layer 3. Then, the electrolyte layer 3 is connected to the anode electrode 2 and the cathode electrode 4.
, And laminated by separators 1 and 5 to complete a molten carbonate fuel cell. In addition, it has been confirmed that a hydrophobizing material such as a paraffinic oil, a naphthenic oil, or a grease-like oil can be similarly used as the fats and oils to make the material hydrophobic. As resins, polyamide resins and the like are also used as hydrophobic materials in addition to fluororesins.

Comparative Example 1 Comparative Example 1 Is a sample prepared for a test to be described later. That is, the material is not hydrophobized by the hydrophobizing material. Lithium carbonate / potassium carbonate (62:38 mol% ratio) mixed powder 4
2 g and γ-lithium aluminate powder (specific surface area: 23
m ² / g) 58 g, polyvinyl butyral 30 g,
94 ml of methanol, 142 ml of n-butanol and 10 ml of butyl butylphenol glycolate were added and kneaded with a ball mill for 15 hours at room temperature to prepare a slurry. The slurry was degassed under reduced pressure by a vacuum pump, and then made into a plate having a thickness of 0.4 mm and a width of 200 mm by a doctor blade method to produce an electrolyte layer. Then, a molten carbonate fuel cell was completed.

Embodiment 3 FIG. 42 g of lithium carbonate / potassium carbonate (62:38 mol% ratio) mixed powder and 58 g of γ-lithium aluminate powder (specific surface area: 23 m ² / g)
17. Naphthenic mineral oil (Sansen Oil # 480)
6 ml was added, and the mixture was kneaded and hydrophobicized by a kneader for 3 hours.
Dry slowly at 50 ° C. for 15 hours. In addition, although it may be left for a long time, Example 1. Or 2. As described above, it is more effective to dry by heat treatment because the production time is shortened.

To this, 5 g of polyethylene oxide, 100 g of polyethylene glycol and 10 g of glycerin were added and kneaded in a ball mill for 20 hours at room temperature to give a viscosity of about 1
A 40 poise slurry was prepared. This slurry was degassed under reduced pressure by a vacuum pump, and then made into a plate having a thickness of 0.45 mm and a width of 200 mm by a doctor blade method.
Was prepared. Then, this electrolyte layer 3 is connected to the anode electrode 2.
And a cathode electrode 4, and further laminated by separators 1, 5 to complete a molten carbonate fuel cell.

Comparative Example 2 Comparative Example 2. These are also used for confirmation experiments to be described later, and have not been made hydrophobic by a hydrophobizing material. 42 g of lithium carbonate / potassium carbonate (62:38 mol% ratio) mixed powder and 58 g of γ-lithium aluminate powder (specific surface area: 23 m ² / g)
Then, 5 g of polyethylene oxide, 160 g of polyethylene glycol and 10 g of glycerin were added and kneaded with a ball mill for 15 hours at room temperature to prepare a slurry having a viscosity of about 140 poise. This slurry was degassed under reduced pressure by a vacuum pump, and then made into a plate having a thickness of 0.45 mm and a width of 200 mm by a doctor blade method to produce an electrolyte layer. And
A molten carbonate fuel cell was completed.

Here, preparation of a slurry by adding and mixing an organic polymer binder and a solvent will be described. The slurry is used because it is suitable for forming the electrolyte layer or the like into a sheet shape, but is not restricted. Using one or more and / or a mixture of two or more kinds selected from polyvinyl butyral, polyvinyl alcohol, polyethylene oxide, polyethylene glycol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, butadiene copolymer, and the like as the organic polymer binder. Can be. These organic polymer binders have excellent thermal decomposition characteristics and are effective as a binder for forming an electrolyte layer.

As the solvent, one and / or a mixed solvent of two or more selected from ethyl alcohol, methanol, butanol, propyl alcohol, methyl isobutyl ketone, toluene, xylene, isopropyl alcohol, glycerin and the like is used. And good. These solvents are
It was confirmed that it is suitable as a slurry preparation material when the raw materials of the electrolyte layer are individually formed into sheets, which will be described later. Furthermore, after hydrophobizing the surface of lithium aluminate or carbonate, it was further hydrophilized with a surfactant or the like to confirm that lithium aluminate and carbonate did not change even when water was applied as a solvent. doing. Furthermore, it has been confirmed that when a small amount of glycerin, phthalic acid ester, dipropyl glycol, or the like is added as a plasticizer when preparing a slurry, moldability is improved.

Embodiment 4 FIG. FIG. 2 is a sectional view showing a molten carbonate fuel cell according to another embodiment of the present invention. Embodiment 4. FIG. Is the configuration shown in FIG. 98 g of γ-lithium aluminate powder (specific surface area: 23 m ² / g)
2 g of oleic acid as fats and oils was added, and mixed with a vibration mill for 3 hours to make them hydrophobic. That is, a hydrophobic lithium aluminate was produced. Then, it heat-dried at 50 degreeC for 1 hour. To this, 30 g of polyvinyl butyral, 94 ml of methanol, 142 ml of n-butanol and 10 ml of butyl butylphenol glycolate were added.
The resulting mixture was kneaded with a ball mill for 15 hours at room temperature to prepare a slurry having a viscosity of about 115 poise. The slurry was degassed under reduced pressure by a vacuum pump, and then formed into a sheet having a thickness of 0.35 mm and a width of 200 mm by a doctor blade method, thereby producing a lithium aluminum sheet 6.

On the other hand, lithium carbonate / potassium carbonate (6
To 95 g of the mixed powder, 5 g of stearic acid as oils and fats was added, and mixed with a vibration mill for 3 hours to make the mixture hydrophobic. That is, a hydrophobic carbonate was produced. Then, it heat-dried at 80 degreeC for 5 hours. To this, 20 g of polyvinyl butyral, 94 ml of methanol, 142 ml of n-butanol and 10 ml of butyl butylphenol glycolate were added and kneaded with a ball mill for 15 hours at room temperature to prepare a slurry. This slurry was degassed under reduced pressure by a vacuum pump, and then 0.3 m thick by a doctor blade method.
m and a width of 200 mm were formed into a sheet to prepare a carbonate sheet 7.

This carbonate sheet 7 (12 cm square) is
The electrolyte layer 3 was produced by sandwiching it between two lithium aluminum sheets 6 (12 cm square) in a sandwich shape. Therefore, in the fourth embodiment. In this case, the electrolyte layer 3 as the hydrophobic electrolyte layer was formed into a sheet. Then, the electrolyte layer 3 is connected to the anode electrode 2 and the cathode electrode 4.
And further laminated by separators 1 and 5 to complete a molten carbonate fuel cell. Here, a slurry viscosity of 100 to 150 poise is suitable, and a doctor blade method is suitable for sheet molding, but the production method is not particularly limited.

Next, a confirmation experiment will be described. Confirmation experiment 1. Examples 1 to 4 and Comparative Examples 1 and 2 described above
Then, each of the prepared electrolyte layers was subjected to a temperature of 50 ° C. and a humidity of 6
It was placed in a 0% constant temperature bath, taken out 24 hours later, and observed. Table 1 shows the results of the confirmation experiment.

[0027]

[Table 1]

From Table 1, it can be seen that the electrolyte layers obtained by mixing the raw materials of the electrolyte layers of Examples 1 to 3 to make them hydrophobic and the electrolyte layers obtained by individually making the raw materials of the electrolyte layers of Example 4 hydrophobic and laminated are: There is no warpage or unevenness even in a constant temperature and humidity chamber,
It turned out to be stable.

On the other hand, Comparative Examples 1 to 3 which were not hydrophobized
The electrolyte layer of No. 2 was deformed. As described above, it has been found that the same effect can be obtained with an electrolyte layer made of a material in which the raw materials of the electrolyte layer are individually made hydrophobic. Therefore, since the raw material can be stocked in the state of the hydrophobicized raw material, it may be more advantageous in terms of production management than the case where the electrolyte layer as a semi-finished product is stocked, which is convenient for handling.

Confirmation experiment 2. Examples 1 to 4 and Comparative Examples 1 to
2, the electrolyte layer respectively prepared, an anode electrode made of Ni-Al, cathode consists NiO-Ag - sandwiched between cathode electrode, to constitute a unit cell of the effective electrode area of 100 cm ^2. This single cell was set in a battery test apparatus, a tightening load of 4 kg / cm ² was applied, and 18% CO ₂ -1 was applied to the anode side.
The temperature was raised at 650 ° C. at a rate of 10 ° C./hour while supplying a 6% H ₂ O-remainder H ₂ mixed gas and a 70% air-30% CO ₂ mixed gas to the cathode side. Next, the change with time in the battery voltage at a load current density of 150 mA / cm ² was examined. Table 2 shows the results of the power generation test.

[0031]

[Table 2]

According to Table 2, the single cells of Examples 1 to 4 are:
It was found that the change over time (decrease) of the cell performance was very small as compared with the single cells of Comparative Examples 1 and 2.

Confirmation experiment 3 Confirmation experiment 2. Was disassembled after power generation was completed, and the electrolyte layer and the like were observed. Table 3 shows the disassembly observation results.

[0034]

[Table 3]

According to Table 3, the observation results show that Examples 1 to
It was found that the single cell of No. 4 had no cracks as compared with the single cells of Comparative Examples 1 and 2, and had excellent quality and high reliability.

From the above examples and confirmation experiments, the following has been found. First, 1 to 15 wt% of a hydrophobic material such as a resin or an oil or fat is added to a lithium aluminate powder and a carbonate powder, and the mixture is stirred and mixed with a vibration mill or a ball mill to make the surface of the powder hydrophobic. Sexualized. Then 50
Dried at ~ 350 ° C for 1-20 hours. It has been found that this hydrophobicization prevents moisture absorption. On the other hand, if the amount of the hydrophobizing material added is 1% or less, the hydrophobization of the lithium aluminate powder and the carbonate powder becomes insufficient, and the suppression of moisture absorption becomes incomplete. Further, it was found that when the addition amount was 15% or more, a problem remained in the dispersibility of the slurry when the electrolyte was formed into a sheet. And about the heat treatment drying temperature, 5
It was also found that when the temperature was 0 ° C. or less, the hydrophobicity of the raw material powder became inhomogeneous.

[0037]

According to the present invention, by making the carbonate and lithium aluminate hydrophobic, moisture absorption of the electrolyte layer can be prevented, and a high quality electrolyte layer can be manufactured. Provided is a molten carbonate fuel cell capable of achieving stable performance and long life.

In addition, there is an effect that the handling and inventory control of the raw material of the electrolyte layer or the electrolyte layer as a semi-finished product are facilitated and the productivity is excellent.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a molten carbonate fuel cell according to one embodiment of the present invention.

FIG. 2 is a sectional view showing a molten carbonate fuel cell according to another embodiment of the present invention.

[Explanation of symbols]

1,5 ... separator, 2 ... anode electrode, 3 ... electrolyte layer, 4 ... cathode electrode, 6 ... lithium aluminum sheet, 7 ... carbonate sheet

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigetoku Mitsushima 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Satoshi Kuroe 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Hitachi, Ltd. Hitachi Research Laboratory (56) References JP-A-6-150947 (JP, A) JP-A-63-76267 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , (DB name) H01M 8/00-8/24

Claims (1)

(57) [Claims] 1. A method for manufacturing a molten carbonate fuel cell comprising an electrolyte layer composed of a carbonate as an electrolyte and a lithium aluminate as an electrolyte holding material, wherein the electrolyte layer makes the carbonate hydrophobic. Molten carbonate characterized in that a hydrophobic carbonate which has been previously hydrophobized by a hydrophobizing material and a hydrophobic lithium aluminate which has been obtained by hydrophobizing the lithium aluminate in advance by a hydrophobizing material are formed into a sheet shape and laminated. A method for manufacturing a salt fuel cell.